Low renin, "normal" aldosterone and hypertension: circadian rhythm of renin, aldosterone, cortisol and growth hormone

Aldosterone release during the sleep-wake cycle in humans

The aim of this study was to assess the relative influence on the 24-h aldosterone profile of the adrenocorticotropic system, primarily modulated by a circadian rhythmicity, and the renin-angiotensin system, which is influenced by sleep. Cortisol, plasma renin activity (PRA), and aldosterone were measured for 24 h in healthy subjects under basal conditions, once with nocturnal sleep and once with a night of sleep deprivation followed by 8 h of daytime sleep. The sleep period displayed high mean aldosterone levels, pulse amplitude, and frequency that were reduced during waking periods. During sleep, aldosterone pulses were mainly related to PRA oscillations, whereas they were mainly associated with cortisol pulses during waking periods. Cross-correlation analysis between sleep electroencephalographic activity in the delta band and aldosterone levels yielded significant results, aldosterone following delta waves by approximately 30 min. This study demonstrates that the 24-h aldosterone profile is strongly influenced by sleep processes. A dual influence, by the renin-angiotensin system during sleep and by the adrenocorticotropic system during wakefulness, is exerted on aldosterone pulses throughout the 24-h period.

Clinical relevance of about-yearly changes in blood pressure and the environment

Changes identified by inferential statistics from summer to winter of high to low arterial blood pressures (BP) have been quantified as a large predictable about-yearly BP swing. This condition of a large annual BP amplitude (LABPA) raises concern about hypotension as well as hypertension and raises new questions regarding appropriate guidelines for diagnosis and treatment. Recommendations made in the fall on the basis of data collected in the summer may be totally inadequate in dealing with the patient's condition in the winter. In order to avoid such mistakes, it is imperative to implement a systematic surveillance of BP in the light of current chronobiological limits. Patients with a large circannual BP amplitude are particularly suited for a study of the underlying hormonal mechanisms. The longitudinal monitoring of their BP is also amenable to the study of environmental influences from near and far.

Diurnal variation of plasma atrial natriuretic peptide in normals and patients with enuresis nocturna

The circadian variation of plasma atrial natriuretic peptide (ANP) in relation to urinary excretion of sodium (UNa) and potassium (UK) as well as clearance of creatinine (Ccrea) was assessed in 15 juvenile patients with enuresis nocturna and compared with 11 age-, sex-, and weight-matched normal subjects. Normal juveniles showed a highly significant diurnal variation (p less than 0.001) of plasma ANP with diurnal peak levels at midnight (0000 hours) and minimum levels at 0400 hours. Enuretic patients showed a similar diurnal rhythmicity with normal levels during day and night. In normals both UNa and UK showed significant diurnal rhythmicity with a marked reduction from daytime to night-time. Although the total diurnal excretions of UNa and UK were similar to normals, patients with enuresis showed abnormal diurnal variation in both UNa (p less than 0.05) and UK (p less than 0.01). The abnormal circadian rhythm of UNa and UK in enuretics seemed to be caused by abnormal tubular handling as similar abnormalities were found in the fractional excretions and as the circadian variation of Ccrea was normal. Especially during the first hours of sleep (2200 hours to 0000 hours), the patients showed polyuria (230 +/- 138 ml vs 116 +/- 58 ml, p less than 0.01), natriuresis (20.9 +/- 16.3 mmol l-1 vs 10.7 +/- 6.8 mmol l-1, p less than 0.01), and kaliuresis (7.3 +/- 6.3 mmol l-1 vs 3.7 +/- 2.3 mmol l-1, p less than 0.05), despite normal levels of plasma ANP. In conclusion, the study describes the diurnal variation of plasma ANP in relation to urinary excretion of sodium and potassium in a juvenile normal population. Patients with nocturnal enuresis show abnormal diurnal rhythmicity in the urinary excretion of sodium and potassium that is not correlated to the plasma levels of ANP.

Nocturnal oscillations in plasma renin activity during sleep in hypertensive patients: the influence of perindopril

In previous studies, we established a strong concordance between nocturnal oscillations in plasma renin activity (PRA) and REM-NREM sleep cycles. To determine whether this relation persists in the case of moderate essential hypertension and if it is influenced by antihypertensive therapies affecting renin release, six normal subjects and six hypertensive patients were studied. The normal subjects underwent one control night. The hypertensive patients were studied during a first night when a placebo was given. Four of them underwent a second night following a single dose of an angiotensin-converting enzyme (ACE) inhibitor, perindopril; and a third night, 45 days later, with the antihypertensive treatment. In addition, two of the patients underwent two night-studies, after a single and repeated doses of a beta-blocker, atenolol, to see whether preventing renin release modified the sleep structure. The relationship between the nocturnal PRA oscillations and the sleep stage patterns persisted in hypertensive patients receiving placebo. In patients who had low PRA levels, the increases associated with NREM sleep were small. However, the mean relative amplitude of the oscillations, expressed as a percentage of the nocturnal mean, was about 60%, which was similar to that in normotensive subjects. Active renin and PRA oscillations were closely coupled. ACE activity profiles displayed damped fluctuations and no systematic relationship with sleep stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian rhythm of prohormone atrial natriuretic peptides 1-30, 31-67 and 99-126 in man

Two peptides consisting of amino acids 1-30 and 31-67 of the N-terminal end of the prohormone of the atrial natriuretic factor (pro ANF), vasodilate aortas in vitro, lower blood pressure in vivo, and have natriuretic properties similar to the atrial natriuretic factor (ANF, amino acids 99-126 of the prohormone). It has been recently discovered that pro ANF 1-30 and pro ANF 31-67 as well as ANF circulate in man. To determine if these three peptide hormones have a circadian variation in their circulating plasma concentrations, eight housestaff volunteers were studied on a day when they were in the hospital for 24 hr. These 5 men and 3 women, ages 25 to 39 had blood samples taken at 0800, 1200, 1600, 2000, 0000, 0400 and 0800 on the following day. One-half of these house officers were up all night while the other half went to sleep from midnight to 0800 and had their 0400 plasma samples drawn while in a supine position. The peak level for all three peptide hormones was at 0400 for both supine and upright subjects. It was concluded that there are circadian rhythms in normal, active people of these three peptide hormones, whose peak levels are at 0400 irrespective of posture.

Diurnal fluctuation in saliva aldosterone concentration

We have measured saliva aldosterone concentration (SA) at frequent intervals in subjects going about their normal daytime activities. Four hourly sampling sufficed to give a reasonable estimate of mean diurnal SA but hourly sampling is necessary if it is desired to study the temporal pattern of SA. In subjects with normal or elevated mean levels, SA fluctuated considerably suggestive of several distinct episodes of aldosterone secretion. Such fluctuations show little correlation with the concentrations in saliva of glucocorticoids (cortisol + cortisone) nor are they consistent with a circadian rhythm of aldosterone secretion. We suggest that they may represent responses to such stimuli as eating, drinking or physical activity, and possibly to other as yet unidentified factors. These observations show the importance of comprehensive diurnal assessment of aldosterone level in physiological and pathological investigations. Because of its non-invasive nature and the high productivity of the assay, measurement of SA is ideally suited for this purpose.

Geriatric hypertension

Hypertension in the elderly is a frequent occurrence and is associated with an increase in cardiovascular complications. Therapeutic drug intervention in diastolic-systolic hypertension is both safe and effective in decreasing cardiovascular morbidity and mortality. Convincing evidence supporting the value of therapeutic intervention in isolated systolic hypertension is not yet available. At present, selection of specific antihypertensive drugs remains empirical because of insufficient controlled trials in elderly hypertensives. Antihypertensive agents should be initiated in smaller dosages and titrated upward slowly with particular care in avoiding orthostatic hypotension. Above all, lifestyle modification should be kept to a minimum and special attention should be given to the patient's quality of life while on drug treatment.

Circadian as well as circannual rhythms of circulating aldosterone have decreased amplitude in aging women

Age differences in the characteristics of the circadian rhythm in circulating radioimmunoassayable aldosterone were studied on nine 20 to 26 year-old and ten 70 to 78 year-old women and ten 23 to 26 year old and ten 70 to 80 year old men in Würzburg, West Germany. These diurnally active-nocturnally resting subjects were sampled every 3 hours for 15 hours. A classical analysis of variance and a multivariate analysis of rhythm characteristics revealed major effects of age exerted on the circadian aldosterone amplitude in women (p = 0.003) but not in concomitantly sampled men. These observations complement the study of circadian and circannual rhythms in 8 young adults (15-21 years), 10 mature adults (29-36 years) and 10 post-menopausal (44-59 years) North American women, sampled at 100 minute intervals for 24 hours, once in each season, and document that the adrenocortical aldosterone-producing system remains rhythmic with at least two frequencies up to the late decades of human life, although in women it may be characterized by a reduction in the extent of spectral change after 70 years of age.

Response of aldosterone and 18-hydroxycorticosterone to angiotensin II in normal subjects and patients with essential hypertension, Conn's syndrome, and nontumorous hyperaldosteronism

Dose-response curves relating plasma angiotensin II (AII) concentration during AII infusion to blood pressure (BP), to plasma aldosterone, and to plasma 18-hydroxycorticosterone were compared in normal subjects and in patients with essential hypertension, Conn's syndrome, and nontumorous hyperaldosteronism. The BP response was steeper than normal in patients with Conn's syndrome and essential hypertension. Before infusion, mean plasma aldosterone concentration was approximately four-fold higher in Conn's syndrome than in the normal group, while that of 18-hydroxycorticosterone was ninefold higher. Neither increased significantly during AII infusion. In essential hypertension, both corticosteroids were within the normal range, but their responses to AII infusion were greater than normal. In the three subjects with non-tumorous hyperaldosteronism, plasma aldosterone and 18-hydroxycorticosterone concentrations were raised, and their responses to AII infusion resembled those found in essential hypertension and were different from those found in Conn's syndrome. This suggests that nontumorous hyperaldosteronism is not a variant of Conn's syndrome. In the response to AII and in other ways, it is indistinguishable from essential hypertension.

Increased 18-hydroxycorticosterone responses to frusemide in essential hypertension

Plasma concentrations of angiotensin II (AII), aldosterone, 18-hydroxycorticosterone and cortisol were measured in seven patients with benign essential hypertension and in seven age-matched control subjects before, and at frequent intervals for 2 h after the intravenous injection of frusemide (40 mg). In the normal subjects, significant increases in the plasma levels of AII, aldosterone and 18-hydroxycorticosterone were apparent from 15 min after diuretic administration. The integrated responses of each hormone to frusemide administration were calculated. Aldosterone and AII responses to the diuretic were closely related, although three hypertensive patients had normal integrated aldosterone responses despite subnormal increases in the plasma concentrations of AII. The integrated 18-hydroxycorticosterone responses were greater in the hypertensive (median 970 nmol.h h-(1).1-(1)) than in the normal subjects (median 180 nmol.h-(1).1-(1)), P<0.05. Some patients with a raised blood pressure appear to have an enhanced adrenal corticosteroid response to frusemide; this probably reflects an increased sensitivity to angiotensin II.

Rhythm characteristics of plasma renin, aldosterone and cortisol in five subtypes of mesor-hypertension

The possible role of the renin-angiotensin system and ACTH in controlling the temporal organization of circadian rhythm of aldosterone was studied in patients with mesor-hypertension (MH) by simultaneous radioimmunological determinations of within-day changes in plasma renin, aldosterone and cortisol. Thirty-nine uncomplicated, untreated mesor-hypertensive patients, divided in subtypes, were examined. The interrelationship between the rhythm components revealed that the circadian cyclicity of aldosterone in both mesor-normotensive and mesor-hypertensive subjects, with either normal or high renin patterns, has a similar timing in acrophase with renin periodicity, which leads the circadian cortisol rhythm. In low-renin mesorhypertensive subjects a circadian rhythm of aldosterone and cortisol, but not of renin, remains demonstrable. The confidence limits of the estimated acrophase for circadian cortisol rhythm do not, however, overlap the confidence arcs of the aldosterone phase. These findings suggest that in normal or high renin MH subjects the aldosterone rhythmicity is mainly controlled by the renin-angiotensin system. Conversely in low-renin MH subjects the temporal organization of the aldosterone circadian sequences seems to be completely independent of renin-angiotensin control.

Aldosterone regulation in primary aldosteronism: influence of salt balance, posture and ACTH

The response of aldosterone to manipulations of the renin-angiotensin and hypothalamic-pituitary-adrenal systems has been studied in thirteen patients with primary aldosteronism due to a single adenoma (ten patients) or bilateral hyperplasia (three patients). The aldosterone response to dietary sodium restriction was small and variable, although urinary aldosterone excretion increased in nine out of twelve studies. The response of patients with hyperplasia could not be distinguished from those with adenoma. All patients were unresponsive to salt loading. By contrast, plasma aldosterone fell in all patients after overnight dexamethasone (1 mg) and increased after brief (1 h) physiological ACTH stimulation. During prolonged erect posture, plasma aldosterone increased in the three patients with hyperplasia and decreased or remained unchanged in patients with ademona. Changes in plasma renin activity were similar in both groups. These studies show that patients with primary aldosteronism, while largely unresponsive to manipulations of sodium balance, retain sensitivity to small and acute changes in ACTH. The different behaviour of patients with hyperplasia to prolonged erect posture cannot be explained by insensitivity to ACTH, but could be due to a relative increase in sensitivity to angiotensin.

Dissociation of the diurnal variation of aldosterone and cortisol in anephric subjects

Diurnal variation of plasma aldosterone and cortisol concentration in man was studied in 13 anephric subjects and 7 normal subjects. All subjects were ambulatory and active throughout the study except during an 8-hour sleep period. Six anephric subjects received Kayexalate (sodium polystyrene sulfonate) during the studies to prevent potassium accumulation and increase in plasma potassium concentration. Diurnal variation of plasma aldosterone concentration with peak and nadir concentrations at 12:00 noon and 12:00 midnight respectively was demonstrated in the studies on normal subjects. Changes in plasma aldosterone concentration were not significantly correlated with changes in plasma concentration but were highly correlated with changes in PRA (P less than 0.001). There was a highly significant correlation between plasma aldosterone and potassium concentration in the anephric subjects studied without Kayexalate administration (P less than 0.001). In the anephric subjects who received Kayexalate, plasma aldosterone and potassium concentration remained stable, and no correlation could be demonstrated. No diurnal variation of plasma aldosterone concentration could be demonstrated in either group of anephric subjects, whereas plasma cortisol concentration varied as in the studies on normal subjects. Conclusion. Diurnal variation of plasma aldosterone concentration is dependent on continued stimulation by the renin-angiotensin system. Loss of this stimulation has no demonstrable effect on the diurnal variation of plasma cortisol concentration.

Increased adrenal sensitivity to angiotensin II in low-renin essential hypertension

Studies were undertaken to determine if the dissociation of aldosterone and plasma renin activity in low-renin essential hypertension is due to altered adrenal responsiveness to angiotensin II. The responsiveness of the adrenal glands to angiotensin II was determined by infusing graded doses of angiotensin II into normal subjects and into patients with essential hypertension and measuring changes in levels of plasma aldosterone in response to the infusion. To minimize the influence of endogenous angiotensin II and ACTH, supplemental sodium and dexamethasone were given before the infusions. Levels of plasma aldosterone and plasma renin activity were determined in normal subjects and in the same patients after the combined stimuli of furosemide and upright posture, a maneuver used to increase the level of endogenous angiotensin II. To determine if the changes in levels of plasma aldosterone during infusion of angiotensin II were due to alteration of the metabolic clearance of aldosterone, the metabolic clearance of aldosterone was measured before and during the infusion of angiotensin II. After sodium loading, dexamethasone treatment, and supine posture, levels of plasma aldosterone of normal subjects and patients with essential hypertension were suppressed equally. In response to the infusion of angiotensin II, the levels of plasma aldosterone of patients with low-renin essential hypertension were significantly higher than those of normal subjects or of patients with normal-renin essential hypertension. After furosemide and upright posture, levels of plasma aldosterone of patients with low-renin essential hypertension were significantly higher than those of patients with normal-renin essential hypertension, despite a blunted response in plasma renin activity of the patients with low-renin essential hypertension. Decreases in metabolic clearance of aldosterone during infusion of angiotensin II were similar in patients with normal-renin essential hypertension and in patients with low-renin essential hypertension and accounted for only a small fraction of the marked increase in levels of plasma aldosterone of patients with low-renin essential hypertension. It is concluded that patients with low-renin essential hypertension have increased adrenal sensitivity to angiotensin II. This increased sensitivity may explain the dissociation of aldosterone and plasma renin activity in low-renin essential hypertension.

Plasma and urinary aldosterone and their interrelations with blood pressure, plasma renin activity and urinary electrolytes in normotensive subjects

Plasma aldosterone (PA), urinary aldosterone excretion (Aldo-U), urinary sodium and potassium excretion and supine and sitting blood pressure (BP) were studied in 120 normotensive subjects. PA was determined after 1 h supine rest (basal PA), after ambulation for 3--4 h (upright PA) and after stimulation with 80 mg frusemide orally (stimulated PA). Aldo-U and urinary electrolytes were measured the day before the PA determinations. PA and Aldo-U were determined by specific radioimmunoassays. Basal PA rose approximately two-fold after upright posture and about three-fold after frusemide stimulation. However, there was a very wide scatter in PA values between individual subjects. A significant correlation existed between basal PA and Aldo-U (r = 0.42), P less than 0.001). Aldo-U decreased with increasing age. The PA values correlated fairly well with the concomitant values for plasma renin activity (r = 0.26--0.40, P less than 0.004 for basal PRA and P less than 0.001) for both upright and stimulated PRA). No relationships could be found between Aldo-U and urinary electrolyte excretions. No correlations were observed between aldosterone and BP.

Circadian rhythm of lithium toxicity in mice

The existence of cyclical (circadian) variations in lithium toxicity in mice was determined. Mice, standardized to a light-dark cycle, were injected with lithium chloride (940 mg/kg) at one of six times (20:00, 24:00, 4:00, 8:00, 12:00, and 16:00) and subsequently observed for mortality over 28 h. A significant (P less than 0.01) time-of-day effect was found for lithium-induced lethality, with highest lethality following injection at 12:00.

Aldosterone response to ACTH stimulation in anephric and non-nephrectomized patients on regular hemodialysis

The effect of ACTH on plasma aldosterone concentration (PAC) and plasma cortisol concentration (PCC) has been investigated in 5 anephric and 6 non-nephrectomized patients on regular homodialysis. Basal PAC was significantly lower (p less than 0.01) in the anephric (mean 37.6 pg/ml) than in the nonnephrectomized group (mean 117.5 pg/ml), whereas basal PCC (18.6 and 16.5 mug/100 ml, respectively) did not differ significantly (p less than 0.05). Following administration of synthetic beta1-24 ACTH, the maximal percentage increase in PAC was significantly lower ( less than 0.001) in the anephric (105%) than in the nonnephrectomized group (286%). The rise in PCC, 118%, in both groups showed no significant difference (p less than 0.05). The higher basal level of PAC and the more pronounced response to ACTH in nonnephrectomized patients correlated with higher basal levels of plasma renin activity compared with the anephric group. An influence of the remaining renin-angiotensin system on the ability to react to an ACTH stimulation is therefore suggested.

Circadian rhythm of the renin-angiotensin-aldosterone system in the rat

The 24 h-course of plasma renin activity (PRA), plasma aldosterone concentration (PAC), plasma corticosterone concentration (PCC) and of the urinary excretion of sodium, potassium and aldosterone was investigated in male Sprague-Dawley rats under different experimental conditions. The data obtained can be summarized as follows: 1. The renin-angiotensin-aldosterone system (RAAS) of the rat is subject to a circadian rhythm which is largely in phase with the well-known rhythm of the pituitary-adrenal axis. This rhythm can be demonstrated in PRA as well as in plasma concentrations and urinary excretion rates of aldosterone. The rhythm of urinary excretion of electrolytes is unlikely to be due to the rhythm of aldosterone secretion. 2. The light-dark cycle is the main synchronizer for these rhythms: inverting the light-dark cycle for 5 weeks entirely inverts the rhythms of all the parameters cited. 3. A dissociation of the rhythms of PRA and PAC can be observed following sodium restriction or dexamethasone treatment. A role of ACTH IN regulating the rhythmic pattern of aldosterone secretion is suggested by the finding that PAC and PCC follow the same pattern of circadian variations under every experimental condition tested. 4. The responsiveness of the RAAS to stimulation or suppression varies with the time of day. 5. It is suggested that experiments ought to be performed not only during the inactive (light hours) but also during the active (dark hours) phase when investigating the RAAS in the rat. This can conveniently be achieved by the use of an animal room with a reversed lighting regime.

Acute and long-term studies of the mechanisms of action of beta-blocking drugs in lowering blood pressure

The antihypertensive effect of intravenous (acute) and oral (long-term) beta-adrenergic blockade with propranolol or pindolol was evaluated in 46 male patients with either borderline (group I; 23 patients) or sustained (group II; 23 patients) essential hypertension. Arterial pressure, plasma renin activity and plasma concentration of aldosterone were determined during continuous recumbency overnight every 30 minutes before and after treatment. Patients of group I exhibited a marked variation of their recumbent plasma renin activity with relatively low values before midnight and large increases early in the morning. In contrast, low plasma renin activity values and only minimal fluctuations in renin were observed in patients of group II. Plasma renin activity had a consistent relationship with blood pressure both after acute (r = 0.79) and long-term (r = 0.4) beta-blockade. In four patients of group I, who had high plasma renin activity and had responded to intravenous propranolol, infusion of angiotensin II inhibitor did not lower pressure. In group I following beta-blockade, day-night profiles of renin were similar to those observed in group II before treatment. Thus in this latter subgroup, low renin profiles might reflect reduced beta-adrenergic activity. Acute as well as long-term beta-blockade consistently eliminated the day-night rhythm of plasma renin activity, but it did not change rhythm of plasma concentration of aldosterone. Plasma concentration of aldosterone was lower in group II but appeared to be inappropriately high relative to renin levels. These observations suggest that in hypertensive patients classified according to blood pressure and recumbent plasma renin activity profiles a significant relationship exists between changes in plasma renin activity and arterial pressure responses. Thus, patients with high renin levels respond better to treatment than patients with low renin levels. We conclude that in the patients studied, sympathetic nervous system activity mainly determined renin levels as well as antihypertensive effectiveness of the beta-blocking drugs.